Chemical treatment of metal

ABSTRACT

A method for preparing metal surfaces for receipt of a coating such as a paint or adhesive (whereby increased coating adhesion and corrosion resistance is achieved) and the treated metal per se, are disclosed. The method comprises contacting the metal surface with various Beta -diketones.

United States Patet l 13,615,888

[72] Inventors Vernon Paul Wystrach [56] Reference Cited d h f d M h f UNITED STATES PATENTS 22:? y mam 1 2,359,407 10/1944 Forder 148/6.l4R [211 App]. No. 855,398 3,449,192 6/1969 Hook l48/6.l4 X [22] Filed Sept. 4, 1969 Primary Examiner-Ralph S. Kendall [45] Patented Oct. 26, 1971 AnorneyFrank M. Van Riet [73] Assignee American Cyanamid Company Stamford, Conn.

[54] CHEMICAL TREATMENT OF METAL 8 clmmsNo DrawlPgs ABSTRACT A method for preparing metal surfaces for [52] U.S. Cl l48/6.l4 R, receipt of a coating such as a paint or adhesive (whereby in- 148/6.27 creased coating adhesion and corrosion resistance is [51] Int. Cl C23f 7/00 achieved) and the treated metal per se, are disclosed. The [50] Field of Search 148/6.l4, method comprises contacting the metal surface with various 6.15, 6.27 B-diketones.

CHEMICAL TREATMENT OF METAL BACKGROUND OF THE INVENTION The use of various chemical materials in the treatment of metal surfaces to thereby render them corrosion resistant is well known to those skilled in varnishes, art. For example, U.S. Pat. No. 1,798,2l8 describes a method whereby certain molybdenum compounds are utilized, whereas U.S. Pat. No. 1,91 1,537 discloses the use of dicarboxylic and hydroxy-dicarboxylic acids for the same purpose. Phosphoric acid salts, (U.S. Pat. Nos. 1,936,533; 1,936,534; 2,952,669) phosphates, (U.S. Pat. Nos. 2,224,695; 2,472,099; 2,769,737) and orthophosphoric acid-chlorinated hydrocarbon solutions, (U.S. Pat No. 2,789,070) have also been disclosed for similar purposes.

While these prior art techniques generally provide acceptable corrosion resistance, they usually fail in regard to the adhesion of surface coatings such as paints, varnishes, enamels, adhesives etc. thereto. Additionally, many of these antiquated systems are severely polluted by water, i.e. when contacted with water they tend to peel, blister etc.

SUMMARY We have found that the adhesion of coatings to metals can be materially increased or strengthened by first treating the metal with a chemical material which is chemisorbed, i.e. chemically reaCted with or absorbed via strong bonds. In this manner, a foundation or integral chemical or chemically bound coating is formed on the metal surface via reaction with the metal, which foundation is then more susceptible to an ultimate or surface coating such as a paint or adhesive, than materials utilized in the past. Our method results in coatings which are more securely bonded or adhered to the foundation layer because the foundation is chemically bonded to the metal and, in a preferred embodiment, an ultimate coating is chemically bonded to the foundation. That is to say, upon treating the metal according to our novel method, a reaction, as mentioned above, causes a strong bonding of the diketone layer to the metal. There then remains, in our preferred embodiment, a second reactive group in the diketone layer, which group is free to react with an exterior surface coating. This free reactive group chemically combines with the surface coating applied thereto to produce a metal having a coating tightly bonded thereto. Additionally, the corrosion resistance of the metal treated according to the present invention, with or without an extraneous coating on its surface, is at least as effective and in many cases, better than known corrosion resistant systems.

DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS Our novel process comprises treating a metal surface, such as that of aluminum, steel, iron, copper, titanium, etc. with a reactive Bdiketone. The useful B-diketones have the formula wherein R and R are, individually, a phenyl group, an alkyl group of 1-4 carbon atoms, inclusive, a benzyl group, a vinyl group, a substituted phenyl group, a substituted alkyl group of 14 carbon atoms, inclusive, or a substituted benzyl group, said substituents comprising NH Ol-I, SH or a polymerizable a, fl-ethylenically unsaturated aliphatic group.

Examples of suitable compounds represented by Formula I, above, include l,3-diphenyl-l,3-propanedione, 1,3-dibenzyll,3-propanedione, l,3-bis-p-hydroxyphenyl)- l ,3- propanedione, l,3-bis(p-amlnophenyl)- l ,3-propanedione, l ,3-bis( p-mercaptophenyl)- l ,3-propanedione, l,3-bis(phydroxybenzyl)-l,3-propanedione, l,3-bis(m-aminobenzyl)- 1,3 l ,3-bis-o-rnercaptobenzyl)- l ,3-propanedione, l,3-bis( pvinylbenzyl)-l,3-propanedione, 2,4-pentanedione, 5,7-undecanedione, l,5-dihydroxy-2,4-pentanedione, 1,5-dlamino- 2,4-pentanedione, l,5-dimercapto-2,4-pentanedione, 1,5- divinyl-2,4-pentanedione, I-benzyl-3-phenyll ,3- propanedione, l-p-hydroxyphenyl-2,4-butanedione, l,l ldihydroxy-S,7-undecanedione and the like. These specific compounds are mentioned herein for purposes of illustration only and the list is not meant to be inclusive of all possible useful compounds.

While not wishing to be bound by any particular theory, we believe that the C 0 groups of the diketones react with the oxide layer formed on the surface of the metal to be treated. The existence of such oxide layers is well recognized by cogent workers in the art. Such layers form upon exposure of the metal to the atmosphere. After the diketone-oxide bonding is complete, the reactive groups of the ketone foundation layer, if any, are then free to react with the surface coating, i.e. paint adhesive etc., thereby chemically bonding the coating to the metal. The diketone-oxide bonding is pseudo-chemical in nature and can be more accurately described as a chemisorption or chelation of the diketone by the metal.

The diketone foundation layer may be applied to the metal surface, the metal first being thoroughly cleaned such as by degreasing with trichlorethylene etc. or other common techniques, by immersing, dipping, painting, brushing, wiping, spraying etc. the metal article to be treated with solutions of one or more of said B-diketones, for a length of time such that the metal surface absorbs or reacts with a sufficient amount of the diketone. The metal is then merely removed from the solution and allowed to dry.

Additionally, the B-diketone can be applied to the metal by first incorporating it into the surface coating material, e.g. the paint or adhesive, and then applying the surface coating. In this manner, the diketone can be added, for example, to the paint vehicle and the paint then can be sprayed etc. onto the metal. Similarly, the diketone can be added to one part of a two-part adhesive system and the adhesive can then be applied to the metal. In each instance, the reactive groups of the surface coating material will react with the appropriate groups of the diketone, if present, while the diketone itself reacts with the oxide on the metal surface, as more specifically described above.

The diketone solution can comprise from about 1 part to about 50 parts of the diketone per 1000 parts of solvent, e.g. ethanol, methanol, water etc. The treatment is preferably conducted at room temperature although higher or lower temperatures may be utilized, if desired. Complete chemisorption of the B-diketone onto the metal surface is generally achieved in from about 10 to about 20 minutes, the lower the diketone concentration, the longer the reaction time necessary.

As mentioned above, when a group reactive with the surface coating or layer is present on the fi-diketone, the foundation layer of B-diketone affords a chemically available site whereby the reactive groups of a paint or adhesive layer may chemically react to thereby form a tightly adhering coating or layer. Examples of paints, adhesives or other coatings which may be used include epoxy paints and adhesives, i.e. those containing chemically available groups; urethane paints and adhesives, i.e. those containing chemically available NCO groups; acrylic paints and adhesives, i.e. those containing chemically available groups; vinyl paints and adhesives, i.e. those containing chemically available CH=CH groups and the like. As is clear from the enumeration of the chemically available groups of the above-mentioned coatings, the available group may be free to react with the available group of the fi-diketone layer previously applied to the metal surface. These reactive groups are explicitly represented, as discussed above, by NH OH, SH and unsaturated aliphatic groups and in the case of epoxy and urethane paints and adhesives would be Nl-l OH or SH substituted groups, while in the case of acrylic or vinyl paints and adhesives, the reactive group of the fl-diketone would be the unsaturated substituent, including vinyl, allyl etc.

The coating, e.g. a paint, can be applied in a condition such that the reaction concurs while the paint vehicle evaporates or in a condition that the paint must more completely polymerize or cure before it forms a useful coating. in the latter case, if the functional group of the B-diketone is such that it initiates polymerization of the paint, the paint may be applied in a prepolymer or semipolymer condition. An example of such a treatment is illustrated by the use of an hydroxy group containing B-diketone and an epoxy prepolymer. In this case, the hydroxy group both reacts with and cures (polymerizes) the epoxy prepolymer.

Additionally, we have found that our novel processing procedure can be utilized in conjunction with known procedures to obtain a pseudo-synergistic effect. For example, we can improve the corrosion resistance of metals treated according to our invention by first treating the metal with an inorganic chromate in a manner known in the art. Furthermore, the chromate (e.g. potassium dichromate; chromic-acid solution, etc.) may be incorporated into the fl-diketone solution of our novel method before treating the metal according to our invention. In this manner the corrosion resistance of the metal is further increased without loss of the enhanced surface coating adherence mentioned above.

The fi-diketones utilized in the present invention are well known to those skilled in the art as are methods for their production. Generally, they may be produced by the crossed Claisen Condensation reaction, see Morrison et al., "Organic Chemistry," Allyn & Bacon, lnc., Boston, 1959, page 703. A typical reaction would proceed according to the equation:

An additional method consists in using a halide according to the equation:

A specific example comprises reacting, according to the formula:

Murti et al., Indian J. Chem, Vol 4, page 396, I966.

The pretreating process and products of the instant invention find utility in military, industrial and consumer fields such as aircraft and ship surfaces, cooling towers, heat exchangers, window screens, siding etc.

The following examples are set forth for purposes of illustration only and are not meant to be construed as limitations on the present invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

EXAMPLE l in determining the corrosion rate according to Table l, a modified polarographic apparatus is used. The apparatus includes an appropriate experimental cell, a potentiostat and recorder. A three electrode system is used: (I) an aluminum electrode; (2) a calomel reference electrode and (3) a platinum counter electrode. The aluminum electrode is 0.030 inch diameter wire which is potted with a commercially available epoxy resin which is then sanded off so that the actual electrode area is the longitudinal cross section of the wire. For the control, the samples are merely untreated electrodes. For Examples 1-5, the freshly polished aluminum electrode is dipped in a solution of the ,Bdiketone for about 10 minutes.

After treatment, the aluminum electrode is placed in the cell and the appropriate electrical connections to the potentiostat made. The electrolyte is a citrate buffer or pH 4.6. The initial potential of the aluminum electrode is then set at 1.0 volts, with respect to the reference electrode. The voltage scan is then turned on. A sweep rate of 0.2 voltsl-minute in the positive direction is used and the current developed is measured on the recorder. The resulting polarization curve, voltage on the x-axis and the current on the y-axis, may then be analyzed to give the corrosion rate.

The method of analysis is that used by Evans et al., .I. Electrochem. Soc. 108, 509 I961 TABLE I Bron down Corrosion potenrnte, mgJ llal, Ex. B-Diketone Solvent rim. day volts Control (no treatment) 6. 43 50 1 2, 4-pentanedione Water. 1. 64 38 2 l-phenyl-l, 3butancdlone .do 0. 58 32 3 l, ili dibenzyl-l, B-propane- .do. 0. 43 42 tone. 4 1-pl1eny1-2, a-pentanedione do 0. 36 40 5- 2, -hexauedione do 1. 00 30 EXAMPLE 6 Cleaned and degreased aluminum panels (3"X5") are treated by dipping in a O.l percent, by weight, solution of 2.4- pentanedione in water for several hours, removed and dried in air. The resultant panels are then exposed in a salt fog test chamber (5 percent salt at F.) for 1000 hours along with untreated control samples. Visual and microscopic investigation of these panels after 1000 hours of exposure indicates that the panels treated with 2,4-pentanedione show a high overall corrosion resistance and very little pitting-type corrosion as compared to the controls.

EXAMPLE 7 Aluminum panels, 3" 5", are degreased by dipping in benzene and further cleaned by dipping in a hot 10 percent solution of a commercially available aluminum cleaner. The panels are then allowed to dry in air. One panel is then immersed in a solution of l,3-bis(p-hydroxyphenyl)-1.3- propanedione in ethanol. After 15 minutes the panel is removed and allowed to dry.

The panel is then spray painted with a commercially available epoxy paint and allowed to dry and cure for 5 days at room temperature.

The painted panel is then subjected to a modified version of the Cross-Hatch Tape Test formulated by the Nationai Coil Coaters Association. In the test, the painted surface is cut times vertically and 10 times horizontally with a razor blade, the scratch lines being approximately 5 mm. apart. Scotch cellophane tape No. 600 is applied over the test area and rubbed with sufficient pressure to remove all air bubbles. The panel is allowed to set for 10 minutes and the tape is then removed sharply with a pull at right angles to the test surface. A visual examination allows a reasonably accurate estimation of the percent finish remaining on the panel in the test area.

The average results of tests conducted on panels treated according to Example 7, in addition to the results recorded utilizing diflerent B-diketones according to the process of the present invention, are set forth in Table ll, below.

Following the procedure of Example 1 except that 3,5-heptanedione is utilized in place of the 2,4pentanedione used therein, a similar corrosion resistant panel is produced.

EXAMPLE 13 Again following the procedure of Example 1, a corrosion resistant panel is produced utilizing 5,7-undecanedione.

EXAMPLE l4 Utilizing the procedure of Example 1 except that 1,3- diphenyl-l,3-propanedione is employed, a corrosion resistant panel is produced.

EXAMPLE [5 The procedure of Example 7 is followed except that 1,3- bis(p vinylphenyl)-l,3-propanedione is utilized as the foundation layer and the surface coating is a commercially available white acrylic paint. A panel similar in surface coating retention to that of said example is obtained.

EXAMPLE 16 The procedure of Example 7 is again followed except that after cleaning the surface of the metal panel with a degreasing agent and an alkali cleaning agent, 3 parts of l,3-bis(phydroxybenzyl)-l,3-propanedione are added to 100 parts of the catalyst-curing agent package of a commercially available, 2-package polyurethane adhesive composition. After blending the contents of the two packages together, the resultant mixture is applied to the clean aluminum panel and cured under the recommended conditions. The adhesive is bonded more tightly to the metal panel than it is on a control specimen formed without the added propanedione.

' EXAMPLE 17 The procedure of Example 7 is again followed except that in place of the epoxy paint used therein, a commercially available epoxy adhesive is used. The bonding ofthe adhesive to the metal is similar to that ofthe paint of said example.

1,5-dihydroxy-2,4-pentanedione is used. Similar results are observed.

EXAMPLE [9 The procedure of Example 16 is followed except that 1,3- divinyl-2,4-pentanedione is utilized in place of the B-diketone used therein and the surface coating applied is in the form of an acrylic paint. The adhesion of the paint to the metal is superior to that of a test sample wherein no pentanedione is present.

EXAMPLE 20 A panel identical to that of Example l8 is produced and coated with a commercially available epoxy paint. The adhesion of the paint to the metal panel is excellent.

EXAMPLE 2l The procedure of Example I5 is again followed except that a commercially available vinyl paint is used in place of that paint of said example and the metal used is steel. T he adhesion of the paint to the steel panel is superior to that of a panel coated without the foundation layer of propanedione.

EXAMPLE 22 The procedure of Example 6 is again followed except that lamino-3,5-octanedione is used. An excellent corrosion resistant panel is produced.

EXAMPLE 23 The procedure of Example 1 is again followed except that the metal treated is stainless steel. Similar results are recorded.

EXAMPLE 24 Following procedure of procedure of Example 6 except that the metal treated is carbon steel, effective corrosion resistance is observed.

EXAMPLE 25 The procedure of Example 7 is followed with replacement of the aluminum panels with similar shaped sections of titanium sheet. The adherence of the epoxy paint to the diketone foundation layer is excellent.

EXAMPLE 26 The use of nickel sheet for the aluminum panel of Example 3 results in a good corrosion resistant panel.

EXAMPLE 27 The process of Example 9 is followed except that a commercially available, corrosion resistant nickel-chromium alloy is used in place of the aluminum panels thereof. The average percent of finish remaining after applying the tape test is 68 percent, 6 panels tested.

We claim:

1. A method which comprises coating a metal surface with a compound having the formula wherein R and R are, individually, a phenyl group, an alkyl group of 1-4 carbon atoms, inclusive, a benzyl group, a vinyl group, a substituted phenyl group, a substituted benzyl group or a substituted alkyl group of l4 carbon atoms, inclusive.

the substituents comprising NH H, SH or a polymerizable ",B-ethylenically unsaturated aliphatic group, at least one of said R and R being a substituted phenyl, a substituted benzyl or a substituted alkyl group.

2. An article of manufacture comprising a metal surface having coated thereon a compound having the formula set forth in Claim 1.

3. A method according to claim 1 wherein the metal surface is coated with said compound and a surface coating containing groups chemically reactive with the substituents of said compound is coated thereon.

4. A method according to claim 1 wherein said compound is coated onto said metal surface as a mixture with a surface coating containing groups chemically reactive with the substituents of said compound.

5. A method according to claim 3 wherein said surface coating is a paint.

6. A method according to claim 4 wherein said surface coating is a paint.

7. A method according to claim 3 wherein said surface coating is an adhesive.

8. An article according to claim 2 wherein said metal is aluminum. 

2. An article of manufacture comprising a metal surface having coated thereon a compound having the formula set forth in Claim
 3. A method according to claim 1 wherein the metal surface is coated with said compound and a surface coating containing groups chemically reactive with the substituents of said compound is coated thereon.
 4. A method according to claim 1 wherein said compound is coated onto said metal surface as a mixture with a surface coating containing groups chemically reactive with the substituents of said compound.
 5. A method according to claim 3 wherein said surface coating is a paint.
 6. A method according to claim 4 wherein said surface coating is a paint.
 7. A method according to claim 3 wherein said surface coating is an adhesive.
 8. An article according to claim 2 wherein said metal is aluminum. 